The present invention relates generally to a start up mechanization for gas turbine engines. Particularly, the present invention relates to an apparatus for the cold starting of a gas turbine engine using a controller and direct current motor, rather than a gearbox.
U.S. Pat. No. 3,769,790 discloses a means to prohibit flow of lubricating oil to the engine by a valve that is energized to dump the lubricating oil driven by the pump driven by the engine, column 1, lines 58-64. The '790 patent employs a gearbox, referred to as a reduction gear arrangement or transmission 18, in the single Figure of the '790 patent. This patent requires the use of a gearbox.
U.S. Pat. No. 6,732,529 discloses a clutch that disengages accessories to avoid delivery of excess fuel and oil into the engine during start-up. However, the disclosed clutch mechanism is limited for use with gearboxes, as described in column 3, lines 5-8 of the '529 patent. The gearbox is illustrated in FIG. 3 of the '529 patent. This patent also requires the use of a gearbox.
Aerospace grade gas turbine engine start power is limited by the size of the energy source, e.g., battery, because energy has to be directed to start the turbine engine, and also to an accessory such as a lubricant pump drive motor to pump lubricant or oil. The battery size can be reduced if less power is required, or, if the distribution of power can be used more efficiently. Therefore, start up mechanization is critical in creating a design, which results in minimum stored energy source, e.g. battery size.
Conventionally, accessories for gas turbine engines can be divided into two categories; those driven by bleed air taken from the compressor section of the engine, and those driven mechanically by an accessory drive shaft and gearbox connected directly to the turbine shaft. The mechanical connection from the turbine shaft may be through an engine-mounted gearbox or through a power takeoff shaft to a remotely mounted gearbox.
Accessories driven by bleed air operate by utilizing high-pressure air that is available for driving aircraft accessories by air motors or air turbines. Compressor discharge air at high pressure and temperature is bled from the engine through ports. This air is ducted as a source of power. It operates accessories such as the air-conditioning units, hydraulic pumps, thrust reverser actuators, and various mechanical actuators in the airplane. Air for cockpit or cabin pressurization is also provided by bleed air from the engine compressor.
On multi-engined aircraft equipped with pneumatic engine starters, one engine is usually started from an auxiliary power unit or a ground air source. Air from this operating engine is bled through a system of ducts in the aircraft to power the starters of the other engines.
Use of an accessory drive gearbox (AGB) is a second method of driving accessories. This apparatus is a direct mechanical drive that is operated by gearing from the compressor-turbine drive shaft. Accessory drives and accessory mounting pads are provided in an engine-mounted, accessory drive gearbox or in a remotely mounted gearbox. On some turbojet engines, accessory pads and mechanically powered drives are also provided in the engine nose section. For dual compressor, axial-flow engines, the main accessory drive gearbox usually receives its power from the high-pressure compressor drive shaft. Mechanically driven accessories may include tachometers, generators or alternators, hydraulic pumps, fuel pumps, oil pumps (also known as lubricant pump drive motors), fuel controls, starters, and water pumps. In the case of AGB-driven accessories, a starter-generator is mechanically coupled to the compressor-turbine drive shaft to rotate the compressor-turbine drive shaft. The compressor-turbine drive shaft, or compressor shaft, is drivably coupled to accessories, such as a fuel pump and a lubricant pump drive motor (LPDM).
A conventional gearbox requires energy from the battery source to drive components, which include gears, shafts, and clutches. Typically, a bevel gear is located at the front end of the compressor shaft; the bevel gear meshes with a planetary gear train, which may be housed in an inlet housing. This planetary gear train transmits low-pressure compressor power through two drive shafts: one to the starter gearbox, the other to the accessory gearbox to drive an idler system. A gear located on an output power shaft interconnects with a 90° pinion gear in the output power shaft support housing. The gears drive the high-pressure section of an accessory gear train.
The gear arrangement of the gearbox that causes energy draw typically includes the bevel gear, being the accessory gearbox drive gear, which is splined internally to accept the accessory gearbox shaft. This drive shaft connects the gear carrier to the accessory gearbox through the 900 pinion gear, which in turn is splined directly to a starter-generator drive gear. The starter-generator drive gear provides drive to all subordinate gears located within the accessory gearbox housing.
The energy required to start the engine, or rotate the compressor, must be in excess of that required to overcome rotor inertia and engine friction and air loads. The starter must produce sufficient torque to start the engine properly. Engines must be rotated and accelerated above a certain minimum rotational and acceleration rates if consistently good starts are to be achieved. The torque characteristics of an acceptable starter must be well above the required minimum.
FIG. 1 is a schematic of a start control scheme according to the prior art. A battery 10 provides power to a full authority digital electronic controller (FADEC) 12, which is operably connected to a starter controller and/or pump controller 14. FIG. 1 shows the starter/pump controller 14 as one integrated controller. However, in some prior art systems, the starter controller may be physically separated from the pump controller. The starter/pump controller 14 is operably connected to a starter generator 16 and a lubricant pump drive motor 18.
As can be gathered from the foregoing background, the accessory gearbox with its many components is heavy and large. Further, the gearbox requires energy to drive the gears, components, and accessories.
Therefore, there is a need for a cold start mechanization that reduces weight, occupies less space, requires less energy, and minimizes stored energy source size.